Design study of a micro illumination platform based on GaN microLED arrays

The design study of a micro illumination tool based on GaN microLED arrays is presented. The high spatio-temporal resolution and the capability of generating fully customized optical patterns that characterize the proposed platform would enable the manipulation of biological systems, e.g., for optogenetics applications. Based on ray tracing simulations, the design aspects that mainly affect the device performance have been identified, and the related structural parameters have been optimized to improve the extraction efficiency and the spatial resolution of the resulting light patterns. Assuming that the device is a bottom emitter, and the light is extracted from the n-side, the presence of mesa-structures on the p-side of the GaN layer can affect both the efficiency and the resolution, being optimized for different values of the mesa-side inclination angle. The full width at half maximum (FWHM) of the extracted spots is mainly determined by the substrate thickness, and the relation between the FWHM and the array pitch represents a criterion to define the resolution. Namely, when FWHM<pitch, the spots are assumed to be resolved, while, when FWHM=pitch, a homogeneous distribution of light intensity is observed. The best performance is obtained when an in-GaN micro-lens array is included in the simulated structure, assuming that the substrate has been removed. The spatial resolution of the generated light pattern results as fully preserved, while the extraction efficiency in the best case is up to three times larger than that of a planar GaN/air interface.